Time-limiting circuit arrangement



Dec. 22, 1953 M. J. scHMx'rz Erm.

TIME-LIMITING CIRCUIT ARRANGEME' Filed Dec. 6, 1949 Patented Dec. 22,A 1953 TIME-LIMITING CIRCUIT ARRANGEMENT Mattheus Jacobus Schmitz and Robert Bertold Buchner, Hilversum, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 6, 1949, Serial No. 131,439

2 Claims.

The invention relates to supervisory circuitarrangements with the use of which a tertiary switching operation is performed or initiated if a primary switching operation is not followed within a predetermined time interval by a secondary switching operation.

Such circuit-arrangements are used inter alieJ in automatic signalling systems so as to prevent common switching equipment being engaged for an unnecessarily long time. Accordingly, they are referred to as time limiting circuit arrangements.

is a rule, registers and/or cord circuits in automatic telephone exchanges comprise one or more time-limiting circuits.

A primary switching operation may consist, for example, in a register or a cord circuit being engaged by a calling subscriber. Ii the subscriber omits to dial (secondary switching operation) within a deiinite time (for example 3Q seconds) after he has received dialling tone, a time-hinting circuit becomes operative, the tertiary switching operation being thus initiated. The tertiary switching operation may consist, for example, in automatic through-connection oi the subscriber to an operator, giving an alarm signal, identification of the subscriber and/or release of the register or the cord circuit.

In certain systems, a time-limiting circuit is used to interrupt the dialling path, if a call is not answered within a given time.

Known time-limiting circuits comprising a thermal relay do not yield satisfactory results in practice, because the switching periods may Vary widely owing to the fact that the temperature of the relay does not immediately reassume its normal value upon disconnection of the circuit.

With other known time-limiting circuits a central time piece periodically, for example every 5 seconds, transmits pulses to time-limiting circuits which count the pulses received upon the occurrence of a primary switching operation and initiate the tertiary switching operation, when the number exceeds a definite limit value. In these arrangements the time-limiting circuits must comprise a pulse counting device for registering the pulses.

It has been suggested to use a time-limiting circuit in which a primary switching operation switches on a charging circuit of a condenser and the condenser is discharged upon the occurrence of a secondary switching operation. However, if the secondary switching operation does not occur within a given time, the condenser becomes charged such that a gas discharge tube coupled to the condenser ignites, causing a relay included in the output circuit of the tube to energize and perform the tertiary switching operation.

It has been found in practice that the time limit is exceeded in a few cases only, so that it is rarely necessary for the discharge tubes to become operative.

rihe invention is based on recognition of the fact that a more economic use is made of the discharge tubes, if instead of associating a discharge tube with each condenser use is made of a common supervisory circuit which with the use of electronic means supervises the condenser voltages of a number of time-limiting circuits.

Such a common supervisory circuit is capable of controlling a large group of time-limiting circuits, so that considerable economy as compared with the known arrangements is ensured.

According to the invention a supervisory circuit-arrangement with the use or which a tertiary switching operation is performed or initiated, if a primary switching operation is not followed within a predetermined time interval by a secondary switching operation, the primary switching operation switching a charging circuit of a condenser, and the normal condition of the condenser being re-established on the occurrence of a secondary switching operation, provision being made of electronic means which respond when the voltage across the condenser passes a deiinite limit value, is characterized in that points of the condenser charging circuits of several time-limiting circuits to be supervised are connected to test contacts of a under switch associated with a common supervisory circuit and are each coupled through a rectiiier to a control-electrode of a first discharge tube of the common supervisory circuit, the rectiiiers being normally cut off and a rectiiier becoming conductive, if the voltage across the associated condenser passes the limit value, in which case the nrst discharge tube response, and by means associated therewith the iinder switch is actuated, a second discharge tube, a control-electrode of which is coupled to a iirst wiper of the finder switch, responding upon a test Contact being reached, the potential or which has passed the threshold value and the movement of the iinder switch being stopped, whilst at the same time by way of a further wiper of the finder switch a revlay of the time-limiting circuit concerned is energized with the result that the tertiary siwtching operation is initiated.

In order that the invention may be more clearly understood and readily carried into effect, it

will now be described more fully with reference to the accompanying diagrammatic drawing, which shows one embodiment of the circuit-arrangement according thereto only those elements being show which are required for understanding the invention.

IThe circuit-arrangement shown in vthe ,drawing comprises a common supervisory circuit CI and one of a number of the time-limiting circuits II to be checked., for example a register.

In the normal position, the contact armp of a relay (not shown) of the register occupies-position I, point ii is at earth potential and condenser Ci is uncharged. .The Joperation:of the arrangement is unchanged, if as an alternative, the right-hand terminal of the condenser k(2li instead of being connected toearthiis "Connected to a point ol fixed potential, i. e. if the condenser were normally charged.

.The .pointi/s. connected .to .the .test .contactD of a finder switc 'its .andiby vwayof.arectier gl, toacliecli LgpointfQ'of .the devcefCI. ".The point normally a potential of "24 .mand therectier gi is cut ofi'. Point .Q iscoupleclin a similar manner through .rectiiers .to .thepointsI K ci further :time-limiting circuits.

On the registerloeing engaged.the-.contactarrn p is nioved intdposition 2,..and at lthesame time contact .qis closed. 'Ehe condenser Ci isslowly charged negatively througha highresistancelll and aresistanceR with the .use'ofabatteryfba The resistance tends to .prevent .contacts nl or .t2 from burning during discharge of `thecondenser "Ci, lhe resistance value of Elm-ay, consequentlyjbe comparativelylow.

The .tiineeconstant .of the .condenser'harging circuit .is chosen .such that, .at `.the -end .of the desired .period fior .example B seconds, Ypoint K has assumedapotentialor 24v vIf it .is-necessary vto constructlong .period time-limiting circuits 'several condenser .charging `circuits may advantageously be connectedlin cascade, so that a condenser of the -following .charging circuit is charged by way ofthe preceding chargingcircuit.

ijf 'the subscriber dials within Vthe ,given time, the-arm p returnsto normal `position i and-condenser 'Ci discharges vby .way .of `resistance R2.

However, if .no dialling .takes rplace during vthe given time, for example, .because .the Yregister .is engaged due to 'the 'fact .that vafsubscribers vreceiver is not replaced correctly .on its rest, the potential oi .point K .drops below 24 v. and rectifier g i becomes conductive sothatthe potentialiofp'oint Qi iikewisedecreased. .The-charging condition oi 'the preceding .charging .circuits is'n'ot affected lthtreby,since theassociated-rectiners are cut oit.

Point Q is connected to the-eontrols-grid-:of la discharge i e Li. The .tube Li, the emission current or which is limited to fsuitalolestrength with the use of resistance Ril included in the cathode lead, is normally :conducting 'and the relayfsincluded inthe anode circuitxis normally energized.

if the potential oi point Q drQpSibelgW-mgg yu the tubeL! is out on2 andrelayA is ;de-.energ`ized. Rest contact completes, through resistance R5, a suplolt7 circuit for the vscreen-:grid fof '.-a second discharge tube L2, which `thus :becomes conducting, so that Yrelay Bin .the anode circuit or" the tube L2 .is energized. -In the normal 'posi'n ion, the lpotential -of the screen-.grid of l2 :is equal to that or the cathode Iand the-.tube L2 :is cut oi.

V'By moving break and make contactbinto the test wiper Dl, 'the 'potentials or" points K of the y'various .charging acirouits.

.For this purpose the control-grid of tubeLZ is coupled to the wiper Di. -In'orderlto fpreventthe charging condition of the condenser chargingicircuits from being disturbed,

the control-,gridand-the wiper have included between thein 'a rectifier g2, which becomes conductive only when the potential or a marking contact reached is lower than -24 v. As soon as the outlet .of YZS is reached, .which vcorresponds to the condenser :charging circuit VVII the .timelimit of whichis exceeded, g2 becomes conducting, so that the potentiaio controlfgrid of .tube .L2 decreases, #tube L2 is out off, vand Vrelay B is f de-energized.

The energizingcircuit of rotary magnet :SM is interrupted and the switchZS stops at the outlet concerned.

Now aicircuitis completed from .earth through rest -contact b, .contact ci, .wiper .E i, ,bank contact E, Winding of relay 'I' of device AII to supply point V2 having a potential or --60 v, Reiay T .is venergized and completes a holding circuit for itself through .ma-ke 'Contact :tl yin serieswithniakecontact q-toze'arth.

ICondenser lCi becomes discharged through resistance 'R2 and Vlmake contact ft2. Point ZK assumes l'earth potential and :tube :Lil becomes again conductive. The contacts .al :and u2 open so that relay C is TVdeenergiaed and contact fCi opens. The common supervisory .circuit 'h'as thus-returneditoiitsnormalfposition.

lRelay however, remains flrl'd through finake contact itl By 'the opening y'or closing fof further contacts (not shown) -of Lrelay the 4desired tertiary switchingoperation is' initiated.

What We claim is:

l. Apparatus responsive to 'irst and second switching operations "in 'a condition wherein .said iirst switching 'operation is succeeded by `said second 'switching operation at an instant beyond fedeterniued time interval for 'initiating va =switching 'operation said apparatus `corn- ;orising plurality 'of 'subordinate circuits, `each provided with "a chargeable jdev'ice .including capacitance, 'means 'to effect charging and discharging or said capacitance vin accordance with said loiret and'second switching .operations .respeci ely, whereby theniagnitude cicliarge depends on the Y:interval between said operations, `a .relay for actuating saidthir switchingioperationand tier; "and a common supervisory cir- :id er." ldinute circuits comprisingnrst i oirdischarge tubesvilth control Y Y igni- 's'to 'conne hecharge.. a -le device/through "sah first 'rectier't'o the. control electrode of said tube and'toa 'rstpoint or'constant `po'tenti'ai 4havin'ga value at which said rectifier 'is rendered 'conductive only when said .capacitance attains 5a "charge corresponding to said predetermined time"interval whereby .the conductivity of said 'first 'tube and the current 'ow 'th erethrough 'varies with the .conductivity of said'first '-rec'tiiier, `means.'operated 'by current ilow variations in 'said'irst tube and connected to said second tube for varying the conductive condition and current oW therethrough accordingly, a rotary switch having rst and second rotatable brushes with respective iirst and second switch banks therefor, each switch bank having a plurality of contacts corresponding to said plurality or" subordinate circuits, the contacts of said rst bank` being respectively connected to said chargeable devices of said subordinate circuits, the contacts of said second bank being respectively coupled through the relays of said subordinate circuits to second points of predetermined potential, electromagnetic means operatively coupled to said switch for rotating said brushes across contacts of respective switch banks, means rendered operative by the current now of said second tube established when said rectier is rendered conductive for energizing said electromagnetic means, means connected to said iii-st brush and connected to the control electrode of said second tube for changing the current ilovv therethrough to de-energize said electromagnetic means to stop said brush rotation when said rst brush touches a contact connected to a particular subordinate circuit whose rectiiier has been rendered conductive, and means rendered operative by said changed current fiow in said second tube to connect said second brush to a point of potential having a value relative to said second point to effect activation of the relay of said particular circuit to initiate the third switching operation.

2. Apparatus, as set forth in claim l, wherein the means connected to said first brush and connected to said second tube for changing the current flow therethrough includes a second rectier which is rendered conductive only when said rst brush touches the Contact coupled to the particular subordinate circuit.

MATTHEUS JACOBUS SCHMITZ. ROBERT BERTOLD BUCHNER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,871,300 Burgener 1 Aug. 9, 1932 1,941,085 Hague Dec. 26, 1933 2,143,971 Brazelton Jan. 17, 1939 

